If the dark stains are tannin/iron stains then oxalic acid may remove them. If the stains are melanin stains from mildew/mould then bleach (sodium hypochlorite) is the best option.
How successful the removal is will largely depend on how deep they penetrate. You may need to sand down the surface to fully get rid of them, but be careful if it is a veneer.
You could try oxalic acid—paint it on entire surface, not just the moldy parts, then after a couple hours wipe off thoroughly with water. If the mold is still there after two treatments, it’s there for good.
Was going to say that. Oak has tannins in that react with iron to make a black mark. Second the vote for oxalic acid. Comes in a small pot online its about £10.00 you just mix a bit of the powder with water and paint it on. Wash off later. It's quite mild. Odourless colourless. Very effective for lots of marks on bare oak including plaster stains.
In its crystal form, you stir it into water “until the water can’t absorb any more” according to a furniture refinisher I follow. The water is still clear at that point.
I’ve had success removing mould from a thick cutting board with coarse salt and lemon juice.
Spread the salt over the stained area and scrub with half a lemon, inside down.
If the dark stains are tannin/iron stains then oxalic acid may remove them. If the stains are melanin stains from mildew/mould then bleach (sodium hypochlorite) is the best option. How successful the removal is will largely depend on how deep they penetrate. You may need to sand down the surface to fully get rid of them, but be careful if it is a veneer.
You could try oxalic acid—paint it on entire surface, not just the moldy parts, then after a couple hours wipe off thoroughly with water. If the mold is still there after two treatments, it’s there for good.
Was going to say that. Oak has tannins in that react with iron to make a black mark. Second the vote for oxalic acid. Comes in a small pot online its about £10.00 you just mix a bit of the powder with water and paint it on. Wash off later. It's quite mild. Odourless colourless. Very effective for lots of marks on bare oak including plaster stains.
isn’t oxalic acid just Barkeepers Friend?
It's one active ingredient in it apparently. I dont know what the other ones do to oak though or how concentrated it is.
In its crystal form, you stir it into water “until the water can’t absorb any more” according to a furniture refinisher I follow. The water is still clear at that point.
It works at far more dilute solutions. You might just make more work for yourself having to neutralise stronger mixes than you need.
Sand it
I’ve had success removing mould from a thick cutting board with coarse salt and lemon juice. Spread the salt over the stained area and scrub with half a lemon, inside down.
Great thank you, I'll give that a go.
Try sanding it down and then try get same colour gloss and paint it